1. Field of Invention
The present invention relates to a semiconductor fabrication process and structure thereof, and particularly to a chip package process and structure thereof.
2. Description of Related Art
In chip packaging techniques, Tape Carrier Package (TCP) is a major method for packaging liquid crystal display (LCD) driver chip (IC) in recent years. However, when bonding chips with relatively thin inner pins, both the fabrications of the tape and the subsequent chip bonding process will become very difficult due to the limitation of the tape material and its structural property. Therefore, Chip on Film (COF) and Chip on Glass (COG) are developed under the demand for thin, light and compact package in future. The current package method of COF employs vertical conduction bonding by the Anisotropic Conductive Film (ACF), eutectic bonding by heat-pressing the bump and shrinkage bonding by heat-pressing and curing the Non-Conductive Polymer (NCP/NCF).
Referring to FIG. 1, a schematic view of a conventional package structure using vertical conduction bonding by the ACF is depicted. The ACF 100 is mainly used to provide an electrical conduction between a gold bump 110 and a contact 120 in the vertical direction by utilizing the conductive effect produced by the deformation of the conductive particle 102 after being pressed. The resin 104 is insulating in horizontal direction. There must be a sufficient amount of conductive particles 102 pressed between the gold bump 110 and the contact 120 to obtain a low contact resistance. At present, the conductive particles 102 may have a particle size as small as 3-5 μm, and are distributed in the resin 104 dispersedly. Thus, it is very possible for the conductive particles 102 in high density to aggregate in the area between the gold bumps 110 and causes a bridge short. Or, the non-uniform distribution of the conductive particles 102 causes an open circuit or different contact resistances. Therefore, the distribution uniformity and density of the conductive particles 102 will influence the electrical performance after the gold bump 110 being bonded with the contact 120.
Next, referring to FIG. 2, a schematic view of a conventional package structure using eutectic bonding is depicted. Eutectic bonding is mainly to bond the gold bump 110 and tin block 122 together by eutectic through applying heat and pressure uniformly. Since the eutectic bonding has high strength and high reliability, and will not cause the problem of bridge short, it therefore can be applied in the package structure with fine contact pitch.
And then, referring to FIG. 3, a schematic view of a conventional package structure using shrinkage bonding by the NCP/NCF is depicted. The shrink force produced by heat-pressing and curing the NCP/NCF 130 maintains a certain contact stress between the gold bump 110 and the contact 120 in conduction; while the thermal expansion of the NCP/NCF 130 in the high-temperature environment may obviously reduce the contact stress between the gold bump 110 and the contact 120, and the contact resistance is thereby increased. Therefore, the thermal expansion and cold shrinkage property of the NCP/NCF 130 will directly influence the electrical performance after the gold bump 110 being bonded with the contact 120.
In view of this, it is an essential issue to enhance the bonding reliability between the gold bump and the contact, based upon the existing chip package techniques, so as to avoid the problems. The problems may influence the electrical performance after the gold bump being bonded with the contact due to, for example, bridge short or thermal expansion and cold shrinkage of the resin.